The US getting more directly involved in Ukraine was never a likely outcome, for reasons that have nothing to do with American public opinion. Throughout the Cold War, both the USA and the USSR made a policy of never directly engaging in conflict on the same soil, because the risk of it escalating into a nuclear war was just too great. Instead, they would fight proxy wars where at most one country was a direct combatant, and the other country merely provided material support to an ally.
We can expect the war in Ukraine to continue following the same playbook, and for the same reason. And other NATO countries will also avoid sending their own troops into Ukraine for fear of creating a slippery slope that pulls NATO's nuclear powers into the war.
America had its own share of propaganda, that brought popular support for those wars... some even very fake one: https://en.wikipedia.org/wiki/Nayirah_testimony America also had hippies and other anti-war groups, so the situation is not that much different.
historically, a majority of Americans supported both the wars in Afghanistan and Iraq when they started, and public opinion did not turn against them for several years, and even then it was not an overwhelming majority.
Obama campaigned on the folly of those wars but chose to stay involved because it was believed by many that some level of success could yet be achieved for the people in those countries, who were in many cases partnering with the US.
Nevertheless, the eventual unpopularity of those wars did in fact lead to "regime change" in the US, because the US is a (somewhat) functioning democracy.
Americans are in fact at this very moment preventing the US from engaging in this war in Ukraine.